Drafting machine head



April 28, 1970 T. LAMB 3,508,336

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I INVENTOR THOMAS LAMB BY MWV/W/ ATTORN S United States Patent 3,508,336 DRAFTING MACHINE HEAD Thomas L. Lamb, Toronto, Ontario, Canada, assignor to The Hughes-Owens Company, Limited, Montreal,

Quebec, Canada Filed Dec. 5, 1968, Ser. No. 781,479 Int. Cl. B431 13/02 U.S. Cl. 33--79 18 Claims ABSTRACT F THE DISCLOSURE Head for drafting machine having a base for connection to a drafting machine linkage. The head includes a rotatable carrier for rules which can be releasa'bly locked with respect-to the base by means of the engagement of complementary tapered surfaces on each. An upper cap portion, when tilted by the draftsman, effects through internal cams releasable engagement of such surfaces so as to permit convenient one hand adjustment of the angular portion of the rules.

BACKGROUND OF THE INVENTION This invention relates to a new and improved drafting head adapted to be carried on drafting machine linkages such as the known arm, track and parallel motion types. In such machines the drafting head provides a mounting for one or more rules which can be rotated about an axis in the drafting head perpendicular to the drawing surface and locked in any desired position of rotation to rule lines on the drawing surface at any required angle.

SUMMARY OF THE INVENTION According to the present invention there is provided a drafting head comprising a base adapted for mounting upon a drafting machine linkage, a carrier assembly mounted to rotate with respect to said base and adapted to support one or more rules in a plane at right angles to the axis of rotation, and locking means selectively operable to lock said carrier assembly in non-rotatable relationship with respect to said base, said locking means comprising a manually engagea'ble actuator element coupled to rotate with said carrier assembly, said actuator element being tiltable with respect to the axis of rotation to effect locking of said carrier assembly with respect to the axis of rotation to effect locking of said carrier assembly with respect to said base. Preferably the base comprises a mounting plate which carries an upstanding hollow body having a bore within which the carrier assembly is rotatably received and the actuator element is an annular cap pivotally connected to the carrier assembly and enclosing the upper portions of the body. Preferably the locking of the carrier assembly is effected by the cam means carried on the annular cap which cooperate with a pair of spaced annular radial surfaces on the hollow 'body to produce a limited axial movement of the carrier assembly relative to the body upon tilting of the annular cap, the locking being achieved by a wedging engagement between mating frusto-conical surfaces on the carrier assembly and hollow body.

The drafting head may in known manner be provided with drawing rules and means such as a protractor for indicating the angular position of the rules with respect to a selected base line.

BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of the invention will now be described by way of example only with reference to the accompanying drawings in which:

FIGURE 1 is a sectional elevation of a drafting head Patented Apr. 28, 1970 ICC DESCRIPTION OF THE PREFERRED EMBODIMENT The drafting head comprises a base 10 formed by a mounting plate 11 having an attachment 12 for mounting the drafting head on a drafting machine linkage (not shown) and a hollow body 13, and a carrier assembly generally indicated at 14 adapted to support a pair of rules 15, 16 which are arranged mutually at right angles as shown in FIGURE 3.

The mounting plate 11 is formed at one end with a large circular aperture which registers with an enlarged annular lower portion of the hollow `body 13 and is seccured thereto as by set screws 17. An annular transparent protector scale 18 marked with angular graduations is rotatably retained between the mounting plate 11 and the lower end of the hollow body, a clamping screw 19 being provided in the mounting plate 11 to clamp the protector scale in non-rotatable relationship to said hollow body 13. The body 13 has a cylindrical bore 20 the upper end of which is counter-bored as at 21 to form an annular step or shoulder 21a, and the lower end of which merges into a short tapered frusto-conical section 22. The upper end of the hollow body 13 carries an annular outwardly extending flange 23 the underside of which faces an annular shoulder 24 also formed on the outside of the hollow body 13.

The carrier assembly 14 is rotatably received within the hollow body 13 and comprises an upper shaft portion 25 and an enlarged lower shaft portion 26 which are secured together by a screw 27 inserted through an axial bore in the lower shaft portion 26 and engaging in a threaded bore in the upper shaft portion 25 as shown in FIGURE l. The upper shaft portion 25 is freely rotatable within the cylindrical bore 20 of the body 13 and has a part of increased diameter which mates with the counter-bore 21 in the body 13 and provides a shoulder 28 adapted to engage the step 21a in the body bore as will be explained. The lower shaft portion 26 has a frusto-conical spigot 29 on its upper side which mates with the tapered portion 22 of the body bore 20, and on an enlarged annular base which lies within the lower portion of the body 13. It will be appreciated that when the upper and lower shaft portions 25, 26 are secured t0 gether by means of the screw 27 when the carrier assembly is retained against removal from the body 13, although it is capable of a limited axial movement relative thereto between abutment of the shoulder 28 on the flange 21a and binding of the tapered spigot 29 in the tapered portion 22 of the body bore 20. A,

The upper shaft lportion 25 is formed with a deep diametral slot 31 extending from the top surface thereof defining two upstanding lim-bs between which is received a depending lug 32 centrally positioned on the underside of an annular cap 33 which has a skirt 34 surrounding and enclosing the upper portion o f the hollow body 13. The lug 32 is pivotally mounted on la pin 35 extending transversely of the diametral slot between the two limbs of the upper shaft portion. On the inner side of the annular skirt 34 are arranged a pair of elongated cams 36 which project inwardly of the skirt and extend between the underside of the body flange 23 and the annular shoulder 24, las can be seen in FIGURES 1 and 2. It will be seen that the annular cap 33 is tiltable on the pivot pin 35 about an axis which is transverse to the rotational axis of the carrier assembly 14 in the hollow body 13, |and this tilting action is employed selectively to lock the carrier assembly in nonrotatable relationship to the hollow body 13. The lug 32 of the y'annular cap 33 is provided with a pair of spaced resilient lingers 37 extending downwardly therefrom towards the bottom of the diametral slot in the upper shaft portion 35 and these fingers act to bias the cap to a position wherein it is substantially coaxial with the hollow body 13 as illustrated in FIGURE 1. In this position the cap 33, and with it the carrier assembly 1.4 including the rules t15 and 16, may be rotated substantially free with respect to the hollow body 13. When it is desired to lock the carrier assembly in non-rotational relationship with respect to the hollow body with the rules 15 and 16 at a selected angular disposition, then the c-ap 33 is tilted with respect to the hollow body, pivoting on the pin 35, clockwise as viewed in FIGURE 2, to bring the lower ends of the cams 36 into engagement with the annular shoulder 24 on the hollow body. It will be noted that the cams 36 are arranged eccentrically with respect to the axis of the pivot pin 35 and therefore upon clockwise tilting of the cap as viewed in FIGURE 2 will move downwards. Upon engagement of the cam 36 with the annular shoulder 24 further tilting force applied to the cap 33 produces a reaction which tends to draw the carrier assembly 14 upwards within the bore of the hollow body and produces a wedging engagement between the tapered spigot 29 of the lower shaft portion 26 and the frusto-conical portion 22 of the body bore 20. This Wedging engagement is sufficient to lock the carrier assembly 14 in non-rotatable relationship with respect to the hollow body 13. The cone angle of taper of the tapered spigot 29 and frusto-conical bore portion 22 to produce the most efficient locking action is dependent upon the materials from which these parts are fabricated. Where both parts are manufactured in -a low friction plastics material such as nylon an angular taper of somewhat less than 5 has been found to give optimum results. In this way an extremely Ipositive reliable locking action between the relative parts is achieved. The cap may be fabricated in 'any suitable material, for example an injection mouldable acetal resin such as Delrin (trademark).

When it is desired to unlock the carrier assembly 14 from the hollow body 13 the cap 33 is tilted in the reverse direction, i.e. counter-clockwise as viewed in FIG- URE 2. This tilting swings the cams 36 upwards out of engagement with the annular shoulder 24 and brings the upper ends of the cams 36 into engagement with the underside of the annular liange 23 at the upper end of the hollow body 13. U-p until this point the carrier assembly remains locked to the hollow body, but upon further tilting movement in the counter-clockwise direction the engagement between the cams 36 and the underside of the flange 23 produces a reaction upon the pivot pin 35 which urges the carrier assembly downwards with respect to the hollow body |13 and disengages the tapered spigot 29 from the frusta-conical portion 22 of the bore 20. This downward movement is limited by abutment of the shoulder 28 of the upper shaft portion 25 upon the step 21a in the hollow bore 20. Hereafter the carrier assembly 14 is free to rotate with respect to the hollow body 13 and upon release of the cap 33 the latter is restored by the resilient fingers 37 to a position wherein it lies coaxial with the hollow body '13.

In normal operation of the drafting head the cap 33 will be gripped by the draftsman in the palm of his left hand and rotated, and tilted to lock and unlock the carrier assembly, by movement of that hand. To provide the draftsman with a ready indication of the tilting direction of the cap this may be provided with a suitable marking provided for rotational adjustment of the protector scale 418 to adjust the base line from which the angular graduations of the scale read. Such means may comprise la transparent window `40 in the mounting plate 11 provided with a marking line `41 to which any selected graduation of the protector scale 18 may be aligned upon release of the clamping screw 19, the drafting head being set to the new base line 4by tightening of the clamping screw 19 when the required protector scale graduation has been aligned with the marking line 41.

The cams 36 are preferably formed integral with the cap 33 and to provide dis-assembly of the cap from the hollow body 13 a pair of notches 42 are provided in the annular flange 23 positioned as indicated in FIGURE 3. It will be appreciated from FIGURE 3 that the notches 42 are so positioned that they do not interfere with the unlocking action of the cams 36 when the cap 33 is in its assembled position, irrespective of the rotational position of the cap.

To dis-assemble the head holes 43 are provided in the skirt 34 of the cap in axial alignment with the pivot pin 35, similar holes (not shown) being provided in the cylindrical wall of the hollow body 13 at the same axial location. The cap is rotated until the pivot pin 35 is aligned with the holes in the cylindrical wall of the hollow body 13 whereupon an instrument can be inserted through the aligned holes on one side to displace the pin 35 axially through the aligned holes on the other side so that this pin may then be withdrawn. With reference to FIGURE 3 the cap 33 can then be moved to the right as shown until the cams 36 are aligned with the notches 42 in the flange 23 whereupon the cap may be lifted from the body. The carrier 'assembly may be dis-assembled by withdrawal of the screw 27 whereupon the upper and lower shaft parts may be separated and withdrawn from opposite ends of the body bore.

What I claim as my invention is:

1. A drafting head comprising a base adapted for mounting upon a drafting machine linkage, said base comprislng a mounting plate which carries an upstanding hollow body having a bore, a carrier assembly received in said bore and mounted to rotate with respect to said base, the carrier assembly being adapted to support one or more rules in a plane at right angles to the axis of rotation, and locking means selectively operable to lock said carrier assembly in non-rotatable relationship with respect to said base, said locking means comprising a manually engageable actuator element coupled to rotate with said carrier assembly, said actuator element comprising an annular cap which encloses at least the upper portions of said body and which is tiltable with respect to the axis of rotation to effect locking of said carrier assembly with respect to said base.

2. A drafting head according to claim 1 wherein said cap is pivotally connected to said carrier assembly on a pivotal axis transverse to said axis of rotation and carries at least one cam which is engageable with an annular radial surface of said body upon tilting of said cap in one direction, to lock said cap and carrier assembly to said body.

3. A drafting head according to claim 2 wherein upon tilting of said cap in the opposite direction said at least one cam is engageable with a second annular radial surface of said body to unlock said cap and carrier assembly for rotation relative to said body.

4. A drafting head according to claim 3 wherein said carrier assembly is movable axially with respect to said body between limits, said carrier assembly having a tapered frusto-conical portion arranged for locking engagement with a mating portion of said bore in the body to limit the relative axial movement in one direction.

5. A drafting head according to claim 4 where the carrier assembly has an upper shaft portion and a lower shaft portion received within said bore and releasably secured together, said tapered frusto-conical portion being provided on one of said shaft portions, -while an abutment shoulder provided on said other shaft portion is arranged to engage a step in said body bore to limit said relative axial movement in the opposite direction.

6. A drafting head according to claim 3 including resilient means operative between said cap and said carrier assembly to bias said against tilting movement towards its locking position.

7. A drafting head according to claim 1 wherein the carrier assembly includes a shaft comprising an upwardly tapering frusto-conical lower portion and a generally cylindrical upper portion both rotatably received in said bore in the hollow body, said annular cap being pivotally connected to the upper portion of said shaft on a pivot axis transverse to said aXis of rotation, said locking means comprising two cams carried at opposed positions on said cap eccentric to the pivotal connection between the cap and the shaft and engageable with an annular radial surface on the outside of said hollow body upon tilting of said cap in one direction, to wedge said frustoconical lower portion of the carrier assembly shaft into engagement with the mating bore of the body to prevent rotation therebetween.

8. A drafting head according to claim 7 wherein a second annular radial surface on said hollow body is engageable by said cams upon tilting of said cap in the opposite direction to disengage said frusto-conical surface of the lower portion of the carrier assembly shaft from the mating bore of the body to free the carrier assembly for rotation relative to said body.

9. A drafting head according to claim 7 wherein the upper and lower portions of said carrier assembly shaft are separable and are releasably interconnected to move together, said upper shaft portion having a peripheral shoulder engageable with a stepped portion in the body bore to limit relative axial movement between the shaft and the body in one direction, relative movement in the opposite direction being limited by the locking engagement between the frusto-conical portion of the shaft and the mating portion of the body bore.

10. A drafting head according to claim 9 wherein the cap has a neutral position intermediate its tilted positions, resilient means being provided operative between the cap and the carrier assembly shaft to bias the cap to its neutral position.

11. A drafting head according to claim 10 wherein said resilient means are formed integral with said cap.

12. A drafting head according to claim 8 wherein at least one of said relatively rotatable members is fabricated in a mouldable plastics material.

13. A drafting head according to claim 8 wherein said body and said carrier assembly shaft are moulded in nylon.

14. A drafting head comprising an upstanding body formed with a bore, a carrier assembly mounted to rotate with respect to said body and having a shaft received in said bore, a frusto-conical surface on said shaft arranged to co-operate with a mating surface in said bore, a manually engageable cap enclosing the upper end of said body and coupled to said shaft to rotate therewith, said cap being coupled to said shaft through a pivotal connection Lwhich permits tilting of said cap about a pivot axis transverse to the rotational axis of said shaft, cam means carried on said cap positioned between opposed first and second annular radial surfaces on said body, said cam means being engageable with said first surface upon tilting of said cap in one direction, to urge said frusto-conical shaft surface axially into locking engagement with its mating bore surface to lock said carrier assembly in nonrotatable relationship to said body, said cam means being engageable with said second surface upon tilting of said cap in the opposite direction to urge said frusto-conical shaft surface axially out of engagement with its mating bore surface and free said carrier assembly for rotation, resilient means operative between said cap and said shaft to bias the cap to a neutral position intermediate said two tilted positions.

15. A drafting head according to claim 14 wherein at least one of said relatively rotatable parts is fabricated in a low friction mouldable plastics material.

16. A drafting head according to claim 14 wherein said body and said shaft are fabricated in nylon and said cap is fabricated in acetal resin.

17. A drafting head comprising a Ibase adapted for mounting upon a drafting linkage, a carrier assembly mounted to rotate with respect to said base and adapted to support one or more rules in a plane at right angles to the axis of rotation, and locking means selectively operable throughout the range of relative rotary movement to lock said carrier assembly in non-rotatable relationship with respect to said base, said locking means comprising a manually engageable actuator means coupled to rotate with said carrier assembly, said actuator means including a cap which is tltable with respect to the axis of rotation between two positions and an element movable into frictional engagement with said base in response to tilting movement of said cap to one of said two positions to effect locking of said carrier assembly with respect to said base at any angularly related location.

18. A drafting head according to claim 17 wherein said base comprises a mounting plate which carries an upstanding hollow body having a ybore within which the carrier assembly is rotatably received, said cap enclosing at least the upper portions of said body.

References Cited UNITED STATES PATENTS 2,243,731 5/ 1941 Eubanks.

FOREIGN PATENTS 990,597 6/ 1951 France.

484,526 10/ 1929 Germany.

HARRY N. HAROIAN, Primary Examiner 

